The present invention relates to a defense system based on a chemical oxygen-iodine laser.
Concerning an iodine laser which emits 1.315 μm radiation from an excited iodine atom I(2P3/2), a Chemical Oxygen-Iodine Laser is called a COIL. The COIL is well known to be able to operate at a high-power CW (continuous wave) mode. In order to operate the COIL, a singlet oxygen molecule (O2(1Δg)) is generated from the chemical reaction of chlorine gas with a BHP solution. The BHP solution is a mixed solution of hydrogen peroxide solution (H2O2) and potassium hydroxide (KOH) or sodium hydroxide (NaOH). The O2(1Δg) is sometimes called singlet oxygen. A reaction chamber to generate the singlet oxygen is usually called SOG (singlet oxygen generator). By mixing the generated O2(1Δg) with iodine molecules, the iodine molecules are dissociated into iodine atoms. Further, the excited iodine atom (I(2P3/2)) is produced by the energy transfer of O2(1Δg) to a basic iodine atom (I(2P1/2)). Thus, a COIL runs the laser operation. Stephen C. Hurlick, et al., “COIL technology development at Boeing,” Proceedings of SPIE Vol. 4631, 101-115 (2002), Masamori Endo, “History of COIL development in Japan: 1982-2002,” Proceedings of SPIE Vol. 4631, 116-127 (2002), Edward A. Duff and Keith A. Truesdell, “Chemical oxygen iodine laser (COIL) technology and development,” Proceedings of SPIE Vol. 5414, 52-68 (2004) and Jarmila Kodymova, “COIL-Chemical Oxygen Iodine Laser: Advances in development and applications,” Proceedings of SPIE Vol. 5958, 595818 (2005) explain about the COIL.
During a COIL operation, singlet oxygen and iodine molecules with a buffer gas, such as helium or nitrogen, are supplied into a laser cavity. At the same time, a vacuum pump is used to pump out effluents, such as deactivated oxygen, iodine molecules and the buffer gas, from the laser cavity. This is because the total pressure in the laser cavity needs to be typically less than about 1000 Pa (about 7.5 Torr).
Chemical lasers have an advantage over other lasers if they are used in space. This is because a chemical laser basically can operate without an electric power supply. Moreover, a vacuum pump is not necessary when a chemical laser is used in space. Therefore, an HF chemical laser is considered to be a primary candidate laser for such a space-based defense system. Jim F. Riker, et al., “An Overview of the Space-Based Laser (SBL) Program,” Proc. SPIE 4632, 181 (2002) explain about space-based lasers. However, it is difficult to use a COIL as a space-based laser because the BHP solution requires gravity force to be gathered in a container of the SOG.
A laser beam from a COIL typically has a poor beam quality, which is another problem with using a COIL as a defense system that requires a high-quality beam in order to propagate for a long distance. This is because a Fresnel number of the laser cavity of a typical COIL is large, which gives a multi-transverse-mode oscillation. For example, a COIL, having a beam diameter of 5 cm and a cavity length of 1 m, gives a Fresnel number of about 475. A conventional COIL is illustrated in FIG. 12. Singlet oxygen generated in a SOG 201 flows in a supply duct 202, passes a laser cavity 203, flows in an exit duct 204, and flows to the outside. Effluent gases such as oxygen and iodine are pumped out to the outside through the exit duct 204 by a vacuum pump (not shown). The laser cavity 203 has a rear mirror 206 and a front mirror 207 from which a laser beam L200a is extracted. As is shown in FIG. 12, the gas flow direction and the optical axis are orthogonal to each other. This makes the cross-section of the extracted laser beam L200a have a rectangular cross-section, not a circular one, which makes it difficult to oscillate at a single transverse mode (TEM00) due to the short laser cavity 203.
The purpose of the present invention is to provide a COIL based defense system, in which a high-power and a high-quality beam can be extracted. Another purpose is to provide a lightweight COIL that can be carried by a high-altitude airship easily. A high-altitude airship is explained by Lewis Jamison, Geoffrey S. Sommer, Isaac R. Porche III, “High-Altitude Airships for the Future Force Army,” Technical Report, The RAND Corporation (2005). A high-altitude airship is briefly shown as a HAA. http://www.rand.org/content/dam/rand/pubs/technical_reports/2005/RAND_TR423.pdf.
Another purpose is to provide a COIL which does not require electric power supply.